Slurry compositions for use in a chemical-mechanical planarization process

ABSTRACT

A chemical-mechanical abrasive composition for use in semiconductor processing uses abrasive particles having a non-spherical morphology.

[0001] This patent application claims the benefit of pending provisionalU.S. patent applications 60/455,216 filed Mar. 17, 2003 and 60/509,445filed Oct. 8, 2003, incorporated herein in their entireties.

FIELD OF THE INVENTION

[0002] The present invention relates to a novel slurry forchemical-mechanical planarization (CMP). The present invention isapplicable to manufacturing high speed integrated circuits havingsubmicron design features and high conductivity interconnect structureswith high production throughput.

BACKGROUND OF THE INVENTION

[0003] In the fabrication of integrated circuits and other electronicdevices, multiple layers of conducting, semiconducting, and dielectricmaterials are deposited on or removed from a surface of a substrate.Thin layers of conducting, semiconducting, and dielectric materials maybe deposited by a number of deposition techniques.

[0004] Common deposition techniques in modern processing includephysical vapor deposition (PVD), also known as sputtering, chemicalvapor deposition (CVD), plasma-enhanced chemical vapor deposition(PECVD), and now electrochemical plating (ECP).

[0005] As layers of materials are sequentially deposited and removed,the uppermost surface of the substrate may become non-planar across itssurface and require planarization. Planarizing a surface, or “polishing”a surface, is a process where material is removed from the surface ofthe substrate to form a generally even planar surface. Planarization isuseful in removing undesired surface topography and surface defects,such as rough surfaces, agglomerated materials, crystal lattice damage,scratches, and contaminated layers or materials. Planarization is alsouseful in forming features on a substrate by removing excess depositedmaterial used to fill the features and to provide an even surface forsubsequent levels of metallization and processing.

[0006] Chemical mechanical planarization, or chemical mechanicalpolishing (CMP), is a common technique used to planarize substrates. CMPutilizes a chemical composition, typically a slurry or other fluidmedium, for selective removal of material from substrates.Considerations in CMP slurry design are discussed in Rajiv K. Singh etal., “Fundamentals of Slurry Design for CMP of Metal and DielectricsMaterials”, MRS Bulletin, pages 752-760 (October 2002). In conventionalCMP techniques, a substrate carrier or polishing head is mounted on acarrier assembly and positioned in contact with a polishing pad in a CMPapparatus. The carrier assembly provides a controllable pressure to thesubstrate urging the substrate against the polishing pad. The pad ismoved relative to the substrate by an external driving force. Thus, theCMP apparatus effects polishing or rubbing movement between the surfaceof the substrate and the polishing pad while dispersing a polishingcomposition, or slurry, to effect both chemical activity and mechanicalactivity.

[0007] Conventional slurries used for CMP processes contain abrasiveparticles in a reactive solution. Alternatively, the abrasive articlecan be a fixed abrasive article, such as a fixed abrasive polishing pad,which maybe used with a CMP composition or slurry that does not containabrasive particles. A fixed abrasive article typically comprises abacking sheet with a plurality of geometric abrasive composite elementsadhered thereto.

[0008] Abrasives which are most extensively used in the semi-conductorCMP process are silica (SiO₂), alumina (Al₂O₃), ceria (CeO₂), zirconia(ZrO₂), and titania (TiO₂), which can be produced by a fuming or asol-gel method, as described in U.S. Pat Nos. 4,959,113; 5,354,490; and5,516,346 and WO97/40,030. There has recently been reported acomposition or a slurry comprising mangania (Mn₂O₃) (European Pat. No.816,457) or a silicon nitride (SiN) (European Pat. No. 786,504).

[0009] U.S. Pat. No. 6,508,952 discloses a CMP slurry containing anycommercially available abrasive agent in particle form, such as SiO₂,Al₂O₃, ZrO₂, CeO₂, SiC, Fe₂O₃, TiO₂, Si₃N₄, or a mixture thereof. Theseabrasive particles normally have a high purity, a high surface area, anda narrow particle size distribution, and thus are suitable for use inabrasive compositions as abrasive agents.

[0010] U.S. Pat. No. 4,549,374 discloses polishing semiconductor waferswith an abrasive slurry prepared by dispersing montmorillonite clay indeionized water. The pH of the slurry is adjusted by adding alkali suchas NaOH and KOH.

[0011] Demands for electrical processing speed have continued toincrease requiring higher and higher circuit densities and performance.It is now desirable to fabricate chips with 8 or more layers of circuitpatterns. In principal the requirement for more layers does not changethe nature of polishing, but it does require more rigorousspecifications from the polishing method. The width of each layer can be<5 μm.

[0012] Defects such as scratches and dishing must be lessened oreliminated. An issue that further increases the technical demand is themove toward 300 mm wafers. The larger wafer makes it more difficult tomaintain uniformity over larger length scales as compared to an 8″, or200 mm, wafer.

[0013] Besides adding layers, increased circuit density can be achievedby decreasing the space between the individual pathways. Pathways cannotbe too close as electrical spillover can occur across the SiO₂dielectric (the wafer oxide) effectively shorting out the connection.Recent technological advancements permitting the fabrication of verysmall, high density circuit patterns on integrated circuits have placedhigher demands on isolation structures.

[0014] US Patent Application Publication 2003/0129838 (filed Dec. 28,1999) discloses the following non-plate-like abrasive materials: ironoxide, strontium titanate, apatite, dioptase, iron, brass, fluorite,hydrated iron oxide, and azurite.

SUMMARY OF THE INVENTION

[0015] High performance polishing is required in the fabrication ofintegrated circuits (ICs) for computer and electronics applications. Inessence, an IC is a device made up of many thin layers sequentiallydeposited on an inorganic oxide wafer. The layers have differentcompositions including oxide, metal, or dielectric materials, and eachmust be polished within narrow tolerances and high selectivity in orderto obtain a working device. Chemical Mechanical Polishing (CMP) is ameans to accomplish this task. Polishing is accomplished via the removalof surface features using a liquid chemical slurry and a rotatingpolymer brush. In an effective system, synergistic relationships betweensurface etching chemicals, surface protecting chemicals, abrasives inthe slurry, and polymer pad physics result in a uniform flat surface. Inthe present invention, particles having a non-spherical morphology areused as the abrasive in a CMP slurry.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is an example of one modified non-spherical particle of thepresent invention.

[0017]FIG. 2 is an example of another modified non-spherical particle ofthe present invention.

[0018]FIG. 3 is an example of a partially coated non-spherical particleof the present invention.

[0019]FIG. 4 is an example of another partially coated non-sphericalparticle of the present invention.

[0020]FIG. 5 is an example of another partially coated non-sphericalparticle of the present invention.

[0021]FIG. 6 is an example of another partially coated non-sphericalparticle of the present invention.

[0022]FIG. 7 is an example of a completely coated non-spherical particleof the present invention.

[0023]FIG. 8 is an example of another partially coated non-sphericalparticle of the present invention.

[0024]FIG. 9 is a depiction of the use of CMP to remove rider from asilicon dioxide layer.

[0025]FIG. 10 is a depiction of polishing an etched semiconductivewafer.

[0026]FIG. 11 is a depiction of polishing an etched wafer containingmetal.

[0027]FIG. 12 is a Scanning Electron Micrograph (SEM) of the ultrafineabrasive particles prepared in Example 1 below.

[0028]FIG. 13 is a graph comparing the removal rate of copper using aCMP slurry containing aluminum oxide and a CMP slurry containingcalcined kaolin particles as the abrasive.

[0029]FIG. 14 is a Scanning Electron Micrograph (SEM) of the ultrafineabrasive particles (Sample A) prepared in Example 3 below.

DETAILED DESCRIPTION OF THE INVENTION

[0030] In general, CMP slurry compositions include abrasives formechanical action and at least one of: oxidizers, acids, bases,complexing agents, surfactants, dispersants, and other chemicals forproviding a chemical reaction such as oxidation on the surface to bepolished. Certain poisons are typically avoided. Examples include metalions with high mobilities, such as Na⁺, or elements that undergoreaction with wafer materials such as fluorine (although HF is sometimesused in post-CMP cleaning).

[0031] Non-limiting examples of available bases include KOH, NH₄OH, andR₄NOH. Acids also can be added, which can be exemplified by H₃PO₄,CH₃COOH, HCl, HF and so on. Available as such supplementary oxidizingagents are H₂O₂, KIO3, HNO₃, H₃PO₄, K₂Fe(CN)₆, Na₂Cr₂O₇, KOCl, Fe(NO₃)₂,NH₂OH, and DMSO. Divalent acids, such as oxalic acid, malonic acid, andsuccinic acid can be used as additives for the polishing composition ofthe present invention.

[0032] Additional suitable acid compounds that may be added to theslurry composition include, for example, formic acid, acetic acid,propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoicacid, oxtanoic acid, nonanoic acid, lactic acid, nitric acid, sulfuricacid, malic acid, tartaric acid, gluconic acid, citric acid, phthalicacid, pyrocatechoic acid, pyrogallol carboxylic acid, gallic acid,tannic acid, and mixtures thereof.

[0033] Suitable corrosion inhibitors that may be added to the slurrycomposition include, for example, benzotriazole, 6-tolylytriazole,1-(2,3-dicarboxypropyl) benzotriazole, and mixtures thereof.

[0034] Carboxylic acids, if added, may also impart corrosion inhibitionproperties to the slurry composition.

[0035] To increase the selectivity of tantalum and tantalum compoundsrelative to silicon dioxide, fluorine-containing compounds may be addedto the slurry composition. Suitable fluorine-containing compoundsinclude, for example, hydrogen fluoride, perfluoric acid, alkali metalfluoride salt, alkaline earth metal fluoride salt, ammonium fluoride,tetramethylammonium fluoride, ammonium bifluoride, ethylenediammoniumdifluoride, diethylenetriammonium trifluoride, and mixtures thereof.

[0036] Suitable chelating agents that may be added to the slurrycomposition include, for example, ethylenediaminetetracetic acid (EDTA),N-hydroxyethylethylenediaminetriacetic acid (NHEDTA), nitrilotriaceticacid (NTA), diethylklenetriaminepentacetic acid (DPTA),ethanoldiglycinate, and mixtures thereof. The chelating agents may aidin the softening of the metallic surface or even help to protect lowlying features or surfaces of particular composition. The idea ofprotection mechanisms may lead to significant improvements.

[0037] Suitable amines that may be added to the slurry compositioninclude, for example, hydroxylamine, monoethanolamine, diethanolamine,triethanolamine, diethyleneglycolamine, N-hydroxylethylpiperazine, andmixtures thereof.

[0038] Suitable surfactant compounds that may be added to the slurrycomposition include, for example, any of the numerous nonionic, anionic,cationic, or amphoteric surfactants known to those skilled in the art.

[0039] The pH of the slurry is vital to the performance of all slurrycomponents. The acidity level of a solution can control reaction ratesat the surface, formation constants of metal complexing agents, rates ofsurface oxidation, solution ionic strength, aggregation size of slurryparticles, and more. Examination of various acids, bases, and pH buffersare a prospective area for CMP development.

[0040] In accordance with the present invention, a CMP slurry isprovided in which the abrasive is formed of particles having amorphology wherein at least one dimension (height, length and/or width)is substantially larger than another. For purposes of this application,such a morphology will be described as “non-spherical.” Thus, anon-spherical particle morphology may be plate-like, sheet-like,needle-like, capsule-like, laminar-like, or any other of a myriad ofshapes having at least one dimension substantially larger than another.Such morphology distinguishes over spherical particles which aresubstantially round in appearance and do not have noticeable elongatedsurfaces. Laminar clays such as kaolin, vermiculite and montmorillonite(that can be exfoliated) and modifications of such clays that preservethe clay shape such as acid leached kaolin, mica, talc, graphite flake,glass flake, and synthetic polymer flake are useful as abrasives in theCMP slurries of this invention.

[0041] These non-spherical particles are primary in the slurry. Thus,the phrase “non-spherical particle” as used herein does not cover anon-spherical agglomeration of spherical particles.

[0042] It is believed that the abrasive particles having a non-sphericalmorphology provide an advantage over the prior art ceramic oxidematerials of spherical shape. It is believed that the pressure of thenon-spherical abrasive on the substrate surface is distributed over anarea rather than a point of contact as the spherical particles.Accordingly, non-spherical particles provide a gentle polishing actionand yet reduce micro-scratching, oxide loss, as well as reduce dishingand erosion compared to the point of contact polishing achieved by thehard ceramic abrasives presently used.

[0043] In addition to having a non-spherical morphology, the abrasiveparticles are preferably softer than the silica or alumina abrasivestypically used for CMP. Accordingly, the non-spherical abrasiveparticles have a Mohs hardness of about 1 to 6. For reference, Table 1below sets forth the various metals and abrasive particles. TABLE 1Microhardness Materials Mohs [kg mm⁻²] Copper 2.5-3.0 80 Tantalum 6.5230 Tungsten 7.5-8.0 350 Hydrated SiO₂ 4-5 400-500 SiO₂ 6-7 1200 CopperOxide 3.5-4.0 — Kaolin (hydrous) 2-3 — Kaolin (calcined) 4.0-6.0 Alumina9.0 2000 ZrO₂ 6.5 — Diamond 10.0  10000

[0044] It is believed that a non-spherical abrasive having a Mohshardness between about 1-6 is hard enough to provide the necessarymechanical action of a CMP slurry, yet defects such as scratching,dishing, and overpolishing action can simultaneously be avoided.

[0045] In general, the non-spherical particle abrasive will comprise upto 20 by weight percent of the slurry although abrasive solids contentsup to 60 wt. % maybe prepared. More typically, amounts of less than 15%by weight and more preferably, an abrasive content in amounts of from0.5-8 wt. % are utilized.

[0046] At present, kaolin clay particles are preferred as thenon-spherical abrasive. While hydrous kaolin can be utilized, it hasbeen found that if the kaolin has been calcined, a better polishing rateresults. However, the overall performance of hydrous kaolin is betterthan calcined kaolin and thus, hydrous kaolin is preferred. Calcinationof the kaolin to undergo a strong endothermic reaction associated withdehydroxylation results in metakaolin. Kaolin clay calcined underconditions more severe than those used to convert kaolin to metakaolin,i.e., kaolin clay calcined to undergo the characteristic kaolinexothermic reaction, results in the spinel form of calcined kaolin andalso mullite if more extreme conditions are utilized. Generally,calcination of the hydrous kaolin at temperatures of 1200° F. and higherresults in the dehydroxylation of hydrous kaolin to metakaolin.Calcination temperatures of 1400-2200° F. can be used to produce akaolin clay that has been calcined through its characteristic exothermto spinel form kaolin. At the higher temperatures, e.g. above 1900° F.,formation of mullite occurs. Any and all of these forms of kaolin claycan be utilized as the abrasive of this invention. All of thesematerials are available commercially from the present assignee,Engelhard Corporation, Iselin, N.J.

[0047] Hydrous kaolin is typically prepared through combination of unitoperations that modify the particle size distribution and removecoloring impurities from kaolin. These unit operations are facilitatedby using aqueous suspensions of kaolin in water. Examples of unitoperations that change the particle size distribution are centrifuges,delamination or milling devices and selective flocculation. Examples ofunit operations that result in removal of coloring impurities areflotation and magnetic separation. Further, reductive and/or oxidativebleaching can be used to render coloring impurities colorless. Inaddition, filtration may be utilized to substantially remove water fromkaolin following which the high solids filtration product slurry can bespray dried. The spray dried portion can be added back to the highsolids filter product slurry to further raise the solids content of theslurry. The filtration product may not be dispersed and thus thefiltercake can be dried and pulverized to obtain what is referred to asacid dried kaolin product in the industry. Additionally, the kaolin maybe modified by thermal or chemical treatments. Typically, the kaolin ispulverized prior to and after the calcinations operation. Treated kaolincan be slurried to further effect modifications to the particle sizedistribution through the unit operations mentioned above.

[0048] Other useful non-spherical abrasive particles are brucite(magnesium hydroxide), hydrotalcite, and nanotalc. The precedingmaterials are commercially available. Other useful non-sphericalabrasive particles are disclosed in commonly assigned U.S. Pat. No.6,187,710 incorporated herein by reference in its entirety. This patentteaches in one embodiment clay minerals made up of elementarythree-layer platelets consisting of a central layer of octahedrallyoxygen-surrounded metal ions (octahedron layer), which layer issurrounded by two tetrahedrally surrounded, silicon atom-containinglayers (tetrahedron layer), characterized in that the dimensions of theclay particles vary from 0.1 micron to one micron. In the octahedronlayer, at most 30 at. % of the metal ions has been replaced by ions of alower valency and in the tetrahedron layers, at most 15 at. % of thesilicon ions has been replaced by ions of a lower valency. The patentteaches in another embodiment that the silicon (germanium) in thetetrahedron layer can be replaced by trivalent ions. In the octahedronlayer, aluminum, chromium, iron (III), cobalt (III), manganese (III),gallium, vanadium, molybdenum, tungsten, indium, rhodium, and/orscandium are preferably present as trivalent ions. As divalent ions,magnesium, zinc, nickel, cobalt (II), iron (II), manganese (II), and/orberyllium are preferably present in the octahedron layer. In thetetrahedron layer, silicon and/or germanium is present as tetravalentcomponent and preferably, aluminum, boron, gallium, chromium, iron (II),cobalt (III), and/or manganese (III) are present as trivalent component.

[0049] The components required for the synthesis, oxides of silicon(germanium) for the tetrahedron layer and the tri/di/monovalent ions forthe octahedron layer, are presented in aqueous medium, are brought tothe desired pH (3-9, preferably 5-9) and are then maintained for sometime at a temperature of 60-350° C., with the pH being maintained withinthe desired range. The reaction time strongly depends on temperature,and hence on pressure, with higher temperatures enabling shorterreaction times. In practice, reaction times to the order of 5-25 hoursare found at the lower temperatures, 60-125° C., whereas at temperaturesin the range of 150° C. and higher, reaction times to the order of someminutes to approximately 2.5 hours may suffice. The reaction time partlydetermines the dimensions of the clay minerals.

[0050] Such a process may be carried out in various ways, depending onthe nature of the components and the desired result. Preferably,chlorides of the metals involved are not worked with, as they lead to areaction into clay minerals that is hardly perceptible, if at all. Formore process details, see incorporated U.S. Pat. No. 6,187,710.

[0051] Another useful non-spherical abrasive particle comprisesexpandable clay platelets that are modified via complexation with othercomponents. The expandable clay systems include smectite clays,montmorillonite, Laponite, Stevensite, and many other natural andsynthetic clays with varying composition, charge density, and plateletdimensions. It is known in the clay literature that these types oflayered materials may be modified by a variety of ion exchange andintercalation processes. Also, positively charged platelets, such ashydrotalcite and other layered double hydroxides, may go through similartypes of chemistry as the negatively charged smectite platelets.

[0052] One example of expandable clay platelets that are modified viacomplexation with other components follows. In FIG. 1, expandable clayplatelets 10 have charged cations 12 such as sodium ions residing in theinterlayer space of the clay platelets. The expandable clay platelets 10are ion exchanged with inorganic clusters 14 such as aluminum oxidehydroxide cation (Al₁₃ Keggin ion) to replace the cations 12. The highercharge density of these resulting clusters yields a stronger interlayerinteraction, and the clay layers remain stacked. The resulting materialis either used without further modification or heated to elevatedtemperatures to form a 3-dimensional pillared structure. Alternatively,positively charged platelets, such as hydrotalcite, may be intercalatedwith anionic clusters such as poly-oxometallates of Mo, W, and othertransition metals.

[0053] Another example of expandable clay platelets that are modifiedvia complexation with other components follows. In FIG. 2, expandableclay platelets 10 have charged cations 12 such as sodium ions residingin the interlayer space of the clay platelets. Organic cations 16, suchas long chain alkyl ammonium ions, are exchanged into the interlayerspaces of smectite or similar negatively charged expandable clayplatelets 10. Alternatively, anionic organic molecules, such asorgano-sulfonates, may be intercalated into the interlayer space ofpositively charged platelets, such as hydrotalcite.

[0054] Another useful non-spherical abrasive particle comprises acentral host that is coated with a secondary component. The central hostmay be a non-spherical particle such as those described above,three-dimensional particles such as alumina or other metal oxideparticle. The coating may partially or completely cover the centralhost. Also, a particle may have multiple coatings on it.

[0055] One example of a partially coated platelet follows. In FIG. 3,host non-spherical particle 18 is partially coated with smallerplatelets 20. Examples of useful smaller platelets 20 include laponiteor other smectite particles or organic polymer coated on the surface ofthe host non-spherical particle 18. A particular smaller platelet mayhave the desired softness and composition, but the platelet size may betoo small or there may be problems with dispersing it. By placing theseplatelets on the surface of the host, with more desirable rheology,dispersion, etc., a more effective abrasive may be developed. Thesetypes of materials may be synthesized by a number of approaches,including layer-by-layer techniques.

[0056] Another example of a partially coated platelet follows. In FIG.4, host non-spherical particle 18 is substantially coated with smallerspherical particles 22. Examples of useful smaller spherical particles22 include colloidal particles such as colloidal silica and molecularspecies such as the aluminum oxide hydroxide Keggin ion. The size,composition, charge density, and other attributes of the smallerspherical particles 22 may be adjusted to meet the desired finalproperties. In addition, different size spheres may be placed on thesurface in subsequent coatings to create different levels of packing,porosity, and softness.

[0057] Another example of a partially coated platelet follows. In FIG.5, host non-spherical particle 18 is substantially coated with smallercrystallites 24. Examples of useful smaller crystallites 24 includemetal oxide or silica crystallites or non-oxide ceramic phases such asmetal carbides and nitrides. Such a coating may be formed by heating toconvert the platelets or colloidal particles into a crystalline oxide.Alternatively, the desired phase may be crystallized directly onto thesurface of the host non-spherical particle 18 similar to knowntechniques for forming titanium dioxide coated mica pearlescentpigments. An example of a useful process is disclosed in commonlyassigned U.S. Pat. No. 4,038,099 incorporated herein by reference in itsentirety.

[0058] Another example of a partially coated platelet follows. In FIG.6, host non-spherical particle 18 is substantially coated with a polymer26. Examples of useful polymers include] diallyldimethylammoniumchloride (abbreviated PDADMAC) or polysodiumstyrene sulfonate(abbreviated PSS). The surface properties such as charge, softness,isoelectric point, rheology etc. may be adjusted by coating the surfaceof the host non-spherical particle 18 with polymer 26.

[0059] An example of a completely coated platelet follows. In FIG. 7,host non-spherical particle 18 is completely coated with carbon 28.Various precursors, such as polymers, organic molecules, etc. maybeplaced on the surface of the host particle 18. The coated material isthen pyrolyzed to form a carbon coating 28. The carbon coating may bevery thin (few nm in thickness) or thick depending on the desiredproperty.

[0060] Another example of a partially coated platelet follows. In FIG.8, host non-spherical particle 18 is partially coated with organicfunctional groups 30. The particle 18 may be treated with couplingagents such as organo-silanes to attach a molecule directly to theparticle surface. Typically, reactive groups on the particle surface,such as hydroxide groups, react with the alkoxy or halo groups of thesilane. The result is the introduction of organic groups with specificfunctionality to the particle surface.

[0061] Particle sizes of the non-spherical abrasive regardless of thetype utilized will typically have an average diameter less than about 1micron as measured by commercially used particle measurement techniques.See for example commonly assigned U.S. Pat. No. 4,767,466 teaching thatparticle sizes are determined with the Sedigraph 5100 particle sizeanalyzer and reported as equivalent spherical diameter on a weightpercentage basis. Kaolin particle size for example is measured by x-raysedimentation, e.g. Sedigraph 5100. The average particle size for kaolinwill preferably range from about 0.01 to less than about 1 micron andmore preferably range from about 0.01 to about 0.5 micron.

[0062] The non-spherical abrasive can be combined with any of thechemical adjuvants which typically form a CMP slurry, such as acids,bases, dispersants, oxidizers, complexing agents, surfactants and/orpassivating agents. The CMP slurry containing the non-spherical abrasiveagent can be utilized in any CMP processing. Examples of typical CMPprocessing are described below. These are intended to be examples onlyand are not provided for the purpose of limiting the uses of the CMPslurries of this invention to the specific processing techniques orconditions disclosed. Thus, the CMP slurries of this inventioncontaining the non-spherical abrasive are intended to be used for any ofthe CMP processes which are now known or can be utilized in the futureas the complexity of the integrated circuits increases.

[0063] For example, in oxide-CMP, the pH of the aqueous solution isadjusted to maintain the suspension of small particles and to soften thesurface of the silicon wafer such that the high features can be groundaway by the action of the abrasives. Depending on the selectedchemistry, the pH of the slurry may be adjusted accordingly. Thus, thepH may be acidic or basic. The surface of the wafer is thought toundergo a transformation under the alkaline conditions as sketched inFIG. 9. As shown in FIG. 9, substrate 32 formed of silicon dioxide istreated by the combination of chemical (alkaline reactivity) andmechanical action (particles abrasion). This situation represents themost straight forward case of oxide-only polishing. Thus, thesilicon-oxide-silicon bonds are broken by the alkaline reaction and theindividual silicon hydroxide moieties on the surface are removed by themechanical abrasive action.

[0064] In order to place an electrical circuit on a chip, a pattern mustbe etched on the wafer surface as in FIG. 10. In this embodiment,substrate 34 has been etched to form a series of channels 36 which canbe filled with dielectric or conductive metal components. The etchedsubstrate 34 increases the challenge of polishing because the surface isnot uniform. The substrate 34 as shown has an etched area of low patterndensity (A) and an area of high pattern density (B). Surface removalduring polishing tends to be greater in areas (B) where the patterndensity is high because the local pressure exerted by the pad isdistributed over less surface area. Other defects such as erosion androunding of sharp corners and features of the pattern must also beminimized.

[0065] Once the wafer containing an etched pattern is prepared, a metallayer can be applied, which will be the electrical circuit. FIG. 11illustrates such a wafer which includes wafer substrate 38, patternedarea or channels 40, and metal or metal alloy 42 contained within thepatterned areas. The metal used is usually a conductive copper/aluminum(Cu/Al) alloy or tungsten (W), which are more resistant to temperatureand oxidation than bulk Cu metal. Polishing is required to remove themetal overburden 44 as the metal layer extends beyond the low lyingetched areas. Metal polishing, as opposed to oxide polishing, isaccomplished using an oxidizing agent in the aqueous solution in orderto form a soft oxide layer on the metal surface that can be removed bythe mechanical abrasives in the slurry. Again, the use of both chemicaland mechanical means are used to polish the surface.

[0066] There are added challenges with metal-CMP. Multiple surfacecompositions are present with varied coverage densities, yet a uniformremoval of metal must be attained. All the overburden metal must beremoved in order to prevent electrical shorts between the circuit lines.Some of the metal surface 42 may undergo metal over polishing within thetrench areas 40 called dishing in FIG. 11. In FIG. 11, LS means linespace while LW means line width. The sum of LW and LS is pitch. LWdivided by pitch is pattern density. An approach to limit dishing is toadd a complexing agent that binds to the low lying metal areas, forminga protective layer and limiting further metal erosion from slurryoxidizers. Clearly, the aqueous slurry and pad composition must bechosen carefully to balance erosion and protection processes.

[0067] Removing excess metal or other contamination from smaller andsmaller spaces between individual pathways presents ever increasingchallenges for CMP processing. Copper metal has a smaller intrinsicresistance and capacitance than Cu/Al alloy, which is currently used asthe conducting medium. Therefore, a smaller electrical potential isrequired to send a signal through a copper line, reducing the tendencyfor electrical spillover. In effect, by using Cu-only, the circuitpathways can be placed closer together.

[0068] However, the use of Cu also has disadvantages. Copper does notadhere well to oxide surfaces. Copper is also susceptible to bulkoxidation as, unlike WO₃ or Al₂O₃, a CuO or CuO₂ surface layer stillallows O₂ and H₂O to penetrate into the bulk metal. Moreover, Cu atomsare mobile and can migrate into the SiO₂ wafer material ultimatelycausing the transistors in the circuit to fail. Therefore, a thin layerof low dielectric material, typically composed of tantalum, tantalumnitride, or titanium nitride, is placed between the wafer oxide andconducting Cu layers. The buffer layer promotes Cu adhesion, preventsoxidation of the bulk Cu metal, prevents Cu ion contamination of thebulk oxide, and further lowers the dielectric between the circuits (i.e.allows the circuits to be even more closely spaced).

[0069] One of the uses of CMP technology is in the manufacture ofshallow trench isolation (STI) structures in integrated circuits formedon semiconductor chips or wafers such as silicon. The purpose of an STIstructure is to isolate discrete device elements (e.g., transistors) ina given pattern layer to prevent current leakage from occurring betweenthem.

[0070] An STI structure is usually formed by thermally growing an oxidelayer on a silicon substrate and then depositing a silicon nitride layeron the thermally grown oxide layer. After deposition of the siliconnitride layer, a shallow trench is formed through the silicon nitridelayer and the thermally grown oxide layer and partially through thesilicon substrate using, for example, any of the well-knownphotolithography mask and etching processes. A layer of a dielectricmaterial such as silicon dioxide is then typically deposited using achemical vapor deposition process to completely fill the trench andcover the silicon nitride layer. Next, a CMP process is used to removethat portion of the silicon dioxide layer covering the silicon nitridelayer and to planarize the entire surface of the article. The siliconnitride layer is intended to function as a polishing stop that protectsthe underlying thermally grown oxide layer and silicon substrate frombeing exposed during CMP processing. In some applications, the siliconnitride layer is later removed by, for example, dipping the article inan HF acid solution, leaving only the silicon dioxide filled trench toserve as an STI structure. Additional processing is usually thenperformed to form polysilicon gate structures.

[0071] The use of Cu and accompanying low dielectric buffer layer demandenhanced performance from polishing techniques. The new techniques arecalled Cu-CMP but in principle do not differ significantly from previouspolishing methods. The CMP process must be able to remove the soft Cumetal overburden, yet limit Cu dishing, scratching, and removal of thelow dielectric buffer layer. Simultaneously, tolerances are morerigorous because of more closely spaced circuit patterns. The ability toproduce layers that are thin, flat, and defect free is of paramountimportance.

[0072] As is also known in the art, one method for forming interconnectsin a semiconductor structure is a so-called dual damascene process. Adual damascene process starts with the deposition of a dielectric layer,typically an oxide layer, disposed over circuitry formed in a singlecrystal body, for example silicon. The oxide layer is etched to form atrench having a pattern corresponding to a pattern of vias and wires forinterconnection of elements of the circuitry. Vias are openings in theoxide through which different layers of the structure are electricallyinterconnected, and the pattern of the wires is defined by trenches inthe oxide. Then, metal is deposited to fill the openings in the oxidelayer. Subsequently, excess metal is removed by polishing. The processis repeated as many times as necessary to form the requiredinterconnections. Thus, a dual damascene structure has a trench in anupper portion of a dielectric layer and a via terminating at the bottomof the trench and passing through a lower portion of the dielectriclayer. The structure has a step between the bottom of the trench and asidewall of the via at the bottom of the trench.

[0073] The abrasive particles of the current invention can be used inCMP of copper in applications other than logic (such as microprocessors)or memory (such as flash memory) devices where copper is used in theinterconnect metallic layers. For example, improving the thermal andelectrical characteristics of the packaging of the device may involveuse of a copper layer that needs to be planarized. The structure of theinterconnect copper layer in the integrated circuit device and thecopper layer in packaging may be different leading to differentrequirements on thickness of layer to be removed, planarity, dishing anddefectivity. Also Micro-ElectroMechanical Systems (MEMS) may have acopper layer that may require planarization using CMP. Abrasiveparticles of the current invention can be used in CMP slurries for thisapplication also.

[0074] A review of CMP processing is provided in “Advances inChemical-Mechanical Planarization,” Rajiv K. Singh and Rajiv Bajaj, MRSBulletin, October 2002, pages 743-747. In general, while the CMP processappears quite simple, achieving a detailed understanding has beenlimited primarily by the large number of input variables in thepolishing process. Among such variables are slurry variables such asparticles and chemicals, pad variables, tool variables such as downpressure and linear velocity, and substrate variables such as patterndensity. The article provides a good review of the process variables andemerging applications for CMP technology and is herein incorporated byreference.

EXAMPLE 1

[0075] Ansilex 93® calcined kaolin slurry (50% solids) supplied byEngelhard Corporation was used as the starting material. The slurry wasmixed with 4 pounds per ton of Defloc 411 (ammonium polyacrylate)supplied by Sharpe Specialty Chemicals. The mixture was Netzsch milledat 1.2 gallons per minute (gpm)—2 passes using zirconia beads. AfterNetzsch milling, 2 pounds per ton of Defloc 411 was again added and themixture then spray dried in order to keep the slurry from spoiling. Thespray dried product was reslurried in a Waring Blender for 5 minutes,then deslimed on the CU5000 (centrifuge) at 40% solids for 26 minuteswide open. Desliming removed the ultrafine fraction of the particulateslurry, which is of interest for the CMP application. The sizedistribution of the spray dried and the ultrafine product as measured bySedigraph 5100 are set forth in Table 2. An SEM of the ultrafineproduct, diluted several times to enhance image quality, is shown inFIG. 12. The SEM was obtained using a field emission electron microscope(Jol 6500F) at 5 kV. TABLE 2 PSD (mass Spray % finer than) Ansilex 93dried product Ultrafine (microns) Slurry Reslurried Product 2 1 92 94100 0.5 79 83 99 0.3 46 58 98 0.2 16 31 85 5 17 65

EXAMPLE 2

[0076] The ultrafine product of Example 1 was reslurried to 4% solids.The slurry was passed through a Puradisc 25 GD glass filter (25 mmdiameter and pore size of 2 microns) to remove oversize particles. Achemical package from a generic Copper CMP slurry was added to theabrasive slurry. The chemical package included an oxidizer (hydrogenperoxide), a passivator (benzotriazole), a complexing/etching agent(citric acid), and a stabilizer (TEA, TX-100). For comparison, acommercial alumina-based CMP slurry (Cabot Microelectronics) was used.

[0077] The CMP slurries were tested on 200 mm Si wafers provided withcopper interconnects and a Ta diffusion barrier by the dual-damasceneprocess. A polishing machine (Novellus IPEC 372) with a down pressure of2 psi was used to apply the CMP slurries. Results are shown in Table 3and FIG. 13. Also, see FIG. 11 for understanding the definitions of“Pitch” and “Pattern Density” used in Table 3. TABLE 3 SurfaceTopography (overpolished area) Alumina Slurry Kaolin Slurry 100 μm Pitch100 μm Pitch 50% Pattern Density 50% Pattern Density Erosion andDishing - severe Erosion <1 nm overpolishing Very low Cu/Ta selectivityGood Cu/Ta selectivity

[0078] The measurements in Table 3 are from the over polished area ofthe wafer. In case of the alumina slurry, severe overpolishing precludedmeasurements on dishing and erosion.

EXAMPLE 3

[0079] A hydrous kaolin spray dried product from Engelhard was used asthe starting material. The spray dried product was reslurried in lab ina Waring Blender for 5 minutes to 40% solids, then deslimed on CU5000centrifuge at 40% solids for 15 minutes wide open (2400 rpms). Theultrafine hydrous kaolin fraction constituting the supernatant at 5%solids from the desliming step was filtered through Whatman filter (25mm diameter and pore size of 2μ) and constituted the abrasive slurry foruse in CMP formulation (Sample A). The size distribution of the startingspray dried product and the ultrafine product as measured by Sedigraph5100 are set forth in Table 4. TABLE 4 PSD (mass % finer Starting Spraydried Ultrafine hydrous than) (microns) product Kaolin (Sample A) 2 98100 1 98 99 0.5 92 98 0.3 73 84 0.18 50 61

[0080] An SEM of the ultrafine hydrous kaolin (Sample A), dilutedseveral times to enhance image quality, is shown in FIG. 12. The SEM wasobtained using a field emission electron microscope (Jeol 6500F) at 10kV.

[0081] Another sample (Sample B) was prepared from a different startingfeed PSD material and after desliming on CU5000 centrifuge at 40% solidsfor 15 minutes wide open (2400 rpms), the ultrafines were furthersubjected to an additional 32 minutes desliming at 2400 rpm and filteredthrough Whatman filter (25 mm diameter and pore size of 2μ). The sizedistribution of the starting spray dried product and the ultrafineproduct as measured by Sedigraph 5100 are set forth in Table 5. TABLE 5PSD (mass % finer than) Starting spray Ultrafine hydrous (microns) driedproduct kaolin (Sample B) 2 88 100 1 80 99 0.5 66 99 0.3 47 93 0.18 3278

EXAMPLE 4 AND COMPARATIVES A AND B

[0082] Chemical package from Example 2 was added to the ultrafinehydrous kaolin slurry (Sample A) from Example 3 to prepare a CMPformulation for planarization of Cu (Example 4). Other CMP formulationswere prepared with the same chemical package by using a fumed silicaslurry and alumina slurry. The fumed silica used was Aerosil 200 fromDegussa (primary particle size of 12 nm and average aggregate size of170 nm as measured by Microtrac)(Comparative A). The alumina particleswere of alpha form and obtained from Polishing Solutions Inc.(Comparative B). The proprietary alumina particles are used incommercial CMP slurries for metal planarization.

[0083] The CMP slurries were tested on bare 200 mmtetraethylorthosilicate (hereinafter “TEOS”) silica wafers as well ascoated with either copper or tantalum to determine the polishing rate toaid in estimating the polishing time for clearing copper on thepatterned wafers, as well as determine surface smoothness andselectivity between copper/tanatalum and copper/silica. The CMP slurrieswere then tested on 200 mm Si wafers provided with copper interconnectsand Ta diffusion barrier by the dual damascene process (patternedwafers) to assess the erosion and dishing. Erosion was measured at 70%patterned density while the dishing was measured on 300 micron pitchcopper line. The dishing and erosion measurements were done on both thepolished and overpolished wafers (20% extra time over polished wafers)to determine sensitivity of these undesirable topographic features tooverpolishing.

[0084] The testing was done on a IPEC-372 M machine (Polishing SolutionsInc., Phoenix, Ariz.) at 5 psi down pressure and 60 rpm platen speed.WIWNU stands for Within Wafer Non Uniformity. Blanket Wafers MaterialTantalum/ Abrasive in CMP Removal Rate Cu/Ta TEOS slurry (nm/min) WIWNU,% Selectivity Selectivity Example 2 254 4.7 65 5.9 Comparative A 206 4.940 1.4 Comparative B 713 10.2 17 2.8

[0085] Clearly, ultrafine hydrous kaolin based CMP slurry resulted inthe desired higher selectivity and uniformity than either fumed silicaor alumina. The copper material removal rate with the ultrafine hydrouskaolin is comparable to fumed silica and lower than that due to alumina.The Cu/Ta selectivity is more critical than the polishing rate since theexpected outcome from the Cu planarization slurry is to stop at the Talayer. The low Ta planarization rate with the hydrous kaolin formulationprecludes from taking advantage of better Ta/TEOS selectivity thansilica or alumina based CMP formulation.

Patterned Wafers

[0086] Just-Polished: estimated by visual inspection of the wafer whencopper is just cleared.

[0087] Overpolished: New patterned wafer polished with 20% extra timeover that required to clear copper. Polished Overpolished ConditionCondition Abrasive in CMP Dishing Erosion Dishing Erosion % increase in% increase in slurry (nm) (nm) (nm) (nm) dishing erosion Example 2 41995 618 74 50 0 Comparative A 450 278 655 386 50 40 Comparative B 332 186522 390 60 110

[0088] The ultrafine hydrous kaolin based CMP slurry resulted insignificantly lower erosion with no sensitivity to overpolishingcompared to silica and alumina. This is consistent with the highselectivity for copper/tantalum and tantalum/TEOS removal rates obtainedwith the ultrafine hydrous kaolin slurry. Thus, compared to silica andalumina, the ultrafine hydrous kaolin slurry is expected to result inlower erosion as well as oxide and metal loss.

[0089] The dishing was similar with all the abrasives indicating astrong role of the chemistry in the formulation compared to themechanical action of the abrasives.

EXAMPLE 5 AND COMPARATIVES C AND D

[0090] In this example, CMP formulations based on ultrafine hydrouskaolin (Sample B) and fumed silica in Example 4 were used with theexception of removal of TX100 and TEA from the chemical package andlowering the slurry pH from 5 to 4 (Comparative C). In addition, analumina-based commercial slurry from Cabot Microelectronics (CCMP) wasalso used (Comparative D).

[0091] The CMP slurries were tested on bare 200 mm TEOS wafers as wellas coated with either copper or tantalum to determine the polishing rateto aid in estimating the polishing time for the patterned wafers,surface smoothness and selectivity between copper/tanatalum as well ascopper/silica. The CMP slurries were then tested on 200 mm Si wafersprovided with copper interconnects and Ta diffusion barrier by the dualdamascene process (patterned wafers) to assess the erosion and dishing.Erosion was measured at 70% patterned density while the dishing wasmeasured on 150 micron width copper line. The dishing and erosionmeasurements were done on both the polished and overpolished wafers (20%extra time over polished wafers) to determine sensitivity tooverpolishing.

[0092] The testing was done on the same machine as in Example 4 and at adown pressure of 2 psi and platen speed of 90 rpm. Blanket WafersAbrasive in CMP Material Removal Rate Copper/TEOS slurry (nm/min) WIWNU,% Selectivity Example 5 173 1 1020 Comparative C 224 1 83 Comparative D127 17 52

[0093] Clearly, ultrafine hydrous kaolin A based CMP slurry resulted inan improved material removal rate and a dramatic improvement inselectivity and uniformity when compared to the commercial slurry.Compared to silica, the removal rate was slightly lower but this factoris far outweighed by dramatic increase in Cu/TEOS selectivity. The veryhigh selectivity is due to extremely low removal rates for TEOS with theultrafine hydrous that results in low erosion and almost no oxide andthus metal loss, which the semiconductor circuit designer has tonormally compensate for in the design.

Patterned Wafers

[0094] Just-Polished: estimated by visual inspection of the wafer whencopper is just cleared.

[0095] Overpolished: New patterned wafer polished with 20% extra timeover that required to clear copper. Polished Overpolished ConditionCondition Abrasive in CMP Dishing Erosion Dishing Erosion slurry (nm)(nm) (nm) (nm) Example 5 405 25 510 32 Comparative C 503 223 466 247Comparative D 131 45 133 70

[0096] The ultrafine hydrous kaolin based CMP slurry resulted in roughly10% of the erosion due to silica and 50% of the erosion due to thecommercial CCMP slurry. The commercial slurry resulted in better dishingcompared to both silica and the hydrous kaolin sample showing theimportance of the optimized chemistry of the formulation.

What is claimed is:
 1. A chemical-mechanical planarization abrasiveslurry comprising primary abrasive particles having a non-sphericalmorphology.
 2. The slurry of claim 1 wherein said abrasive particleshaving a non-spherical morphology are selected from mica, talc, laminarclays, graphite flake, glass flake, and synthetic polymer flake.
 3. Theslurry of claim 2 wherein said abrasive particles comprise laminar clay.4. The slurry of claim 3 wherein said clay particles have been calcinedat a temperature of at least 1200° F.
 5. The slurry of claim 1 whereinsaid slurry comprises up to about 20 weight % of said abrasiveparticles.
 6. The slurry of claim 5 wherein said slurry comprises about0.5 to about 8 weight % of said abrasive particles.
 7. The slurry ofclaim 1 wherein said abrasive particles have an average diameter of lessthan about 1 micron.
 8. The slurry of claim 7 wherein said abrasiveparticles have an average diameter of about 0.01 to about 0.5 micron. 9.The slurry of claim 1, wherein said abrasive particles have a Mohshardness within the range of about 1 to about
 6. 10. The slurry of claim1 wherein said non-spherical abrasive particles have been modified viacomplexation with other components.
 11. The slurry of claim 10 whereinsaid modified non-spherical abrasive particles are substantiallyseparated by inorganic cations.
 12. The slurry of claim 1 wherein saidnon-spherical abrasive particles are at least partially coated.
 13. Theslurry of claim 12 wherein said non-spherical abrasive particles are atleast partially coated with platelets, polymer, carbon, organicfunctional groups, or crystallites.
 14. A method of planarizing asemiconductor with a chemical-mechanical abrasive slurry, saidsemiconductor comprising a surface of semiconductive material, metal,dielectric material or mixtures thereof, said method comprisingcontacting said surface with said chemical-mechanical abrasive slurry,said chemical-mechanical abrasive slurry comprising a primary particleabrasive having a non-spherical morphology.
 15. The method of claim 14wherein said particle abrasive is selected from mica, talc, laminarclays, graphite flake, glass flake, and synthetic polymer flake.
 16. Themethod of claim 15 wherein said particle abrasive is laminar clay. 17.The method of claim 16 wherein said clay has been calcined at atemperature of at least 1200° F.
 18. The method of claim 14 wherein saidslurry contains up to about 20% by weight of said particle abrasive. 19.The method of claim 14 wherein said slurry comprises from about 0.5 toabout 8 weight % of said particle abrasive.
 20. The method of claim 14wherein said particle abrasive has an average diameter of less thanabout 1 micron.